1. Field of the Invention
The present invention relates to a semiconductor device.
2. Description of Related Art
The speed of handling signals has been increasing in recent semiconductor devices such as a DRAM (Dynamic Random Access Memory). The increase in the speed of signals makes a switching element (e.g., a CMOS (Complementary Metal Oxide Semiconductor)) in an internal circuit, such as an output circuit which outputs data to outside a semiconductor device, more susceptible to noise (SSN: Simultaneous Switching Noise) generated by switching.
An internal circuit in a semiconductor device is generally provided between a power line at a power potential and a ground line at ground potential and is supplied with power via the lines. If such an internal circuit is an output circuit or a circuit which needs to output many bits of data in parallel, such as a pre-stage circuit which supplies data to an output circuit, many of the switching elements that constitute the circuit may switch simultaneously. In this case, an abrupt current change occurs between a power line and a ground line, resonance current is generated due to the inductance component of lines for supplying power to the internal circuit, a parasitic capacitance (capacitance component) of the internal circuit, and the like, the difference in potential between the power line and the ground line varies, and noise is generated.
JP2008-85321A discloses a technique for reducing noise generated due to resonance current by providing a capacitive element whose capacitance can be changed between a power line and a ground line, for detecting the strength of noise generated due to resonance current, and for adjusting the capacitance of the capacitive element on the basis of the detection result.
JP2011-9291A discloses a technique for reducing the effect of the generation of resonance current by providing a capacitive element and a switch connected in series with the capacitive element between a power line and a ground line and, if the frequency of the resonance current falls within a predetermined range, shifting the frequency of the resonance current by turning the switch, on or off.
In some cases, in order to reduce resonance current generated in the above-described manner, an output circuit that consists of an internal circuit and a pre-stage circuit provided in front of the output circuit are supplied with power via different lines so as to prevent noise generated in the pre-stage circuit or the like from reaching the output circuit. The present inventors have recognized that, even if an output circuit and a pre-stage circuit are supplied with power by different lines, as described above, resonance current may be generated due to, e.g., an inductance component between a first line for supplying power to the output circuit and a second line for supplying power to the pre-stage circuit, resonance current may cause a difference in potential between the first line and the second line to vary, and noise may be generated.